This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-76035 filed on Mar. 17, 2000.
1. Field of the Invention
The present invention relates to a check valve provided in an engine fuel supply system for preventing the fuel from flowing-back from an engine to a pump.
2. Description of Related Art
In a fuel supply system for a vehicle engine, a check valve is provided at a discharge side of a pump for preventing the fuel from flowing-back to the pump while the engine does not operate, so that pressure of the fuel remaining at the engine side is highly maintained approximately equal to a pressure during a pump operation.
In a conventional check valve, a single valve body is slidably contained in a housing. When the pump operates, the valve body is urged by pressure of the fuel discharged from the pump to open a valve opening. When the pump stops operating, the valve body is urged by pressure of the fuel remaining at the engine side to close the valve opening. While the pump does not operates, the valve body keeps on closing the valve opening, so that the fuel remaining at the engine side is prevented from flowing back to the pump. Thereby, the pressure of the fuel is highly maintained approximately equal to a pressure during a pump operation.
In view of an environmental protection, it is required to reduce a gas fuel leakage from the fuel supply system for a vehicle. The gas fuel leakage increases as the fuel pressure becomes high. Thus, when the engine does not operate, it is desired to maintain the fuel pressure as low as possible as long as the engine normally starts. Further, for improving an engine performance, it is required to increase a discharge pressure of a pump used for a fuel supply system.
However, when the engine stops operating, the conventional check valve still maintains the high fuel pressure at the engine operation. Further, just after the engine stops, the fuel inside the pipe is thermally expanded due to an engine heat, and the pressure thereof may rise over a fuel pressure at the engine operation. The conventional check valve does not suppress the rising of the fuel pressure.
A first object of the present invention is to decrease an engine side fuel pressure when a pump stops operating and maintain the engine side fuel pressure lower than a fuel pressure during the pump operation.
A second object of the present invention is to release the engine side fuel to the pump to prevent the engine side fuel pressure from rising abnormally even when the engine side fuel is thermally expanded due to an engine heat just after the engine stops.
According to the present invention, a check valve is provided in a fuel supply system for en engine, and the check valve comprises a valve casing, a pressure adjusting valve, an urging means, and a check valve body. The valve casing includes a first valve seat. The pressure adjusting valve body is slidably provided in the valve casing, and includes a fluid passage thereinside and a second valve seat. The urging means urges the pressure adjusting valve body toward the first valve seat. The check valve body is provided in the valve casing, and moves with respect to the second valve seat.
When the pump operates, the check valve body leaves the second valve seat due to a pump side fuel pressure for opening the fluid passage inside the pressure adjusting valve body. When the pump does not operate, the check valve body contacts the second valve seat due to an engine side fuel pressure for closing the fluid passage inside the pressure adjusting valve body, thereby preventing the engine side fuel from flowing-back to the pump. When the pump stops operating and the engine side fuel pressure exceeds a pressure corresponding to an urging force of the urging means, the pressure adjusting valve body leaves the first valve seat with the check valve body, so that a gap is provided between the pressure adjusting valve body and the first valve seat. The engine side fuel having the excess pressure is released through the gap. Further, when the fuel thermally expands due to an engine heat, the expanded fuel is released through the gap. In this way, the engine side fuel pressure is maintained at a pressure corresponding to the urging force of the urging means.